Updated with stock price. FOSTER CITY, Calif. ( TheStreet) -- Gilead Sciences ( GILD) surprised investors Thursday night with exciting new data from its lead hepatitis C drug that overshadowed a disappointing fourth-quarter earnings and weaker-than-expected guidance for the coming year. Gilead shares are up 9% to $54.07 in Friday afternoon trading. On Gilead's quarterly conference call, the company's research chief disclosed that all genotype 1 hepatitis C patients treated with the experimental pill GS-7977 plus ribavirin had no evidence of the virus after four weeks of treatment. These new data are early but impressive because they suggest that a two-drug combination of pills may be potent enough to cure patients with genotype 1 hepatitis C, which is the most common form of the disease in the United States. Gilead acquired rights to GS-7977 (formerly PSI-7977) through the $11 billion acquisition of Pharmasset. The deal pushed Gilead to the front of the pack of companies seeking to develop an all-oral regimen for hepatitis C that does away with the need for weekly injections. Bristol-Myers Squibb ( BMY) is paying $2.5 billion to acquire Inhibitex ( INHX) for the same reason. Further data supporting GS-7977's ability to definitively cure these genotype 1 hepatitis C patients will be presented at the Conference on Retroviruses and Opportunistic Infections (CROI) being held March 5-8 in Seattle. Gilead's new GS-7977 data announced Thursday night come from a phase II study known as Electron first started by Pharmasset. In this particular arm of the study, 35 patients with genotype 1 hepatitis C (25 treatment-naïve patients and 10 who failed to respond to previous therapy) were treated with GS-7977 plus ribavirin. After four weeks of this two-drug oral therapy, 100% of patients achieved what is known as a "rapid viral response" or RVR, meaning that the virus could no longer be detected in their blood. RVR is an early and promising signal that drugs are working but it is not definitive proof of a hepatitis C cure. Patients are only deemed cured of hepatitis C -- a sustained virologic response or SVR -- if they have no evidence of the virus in their system 12 weeks after stopping treatment. At the upcoming CROI meeting Gilead will present further results on some of these 35 patients, specifically showing how many have undetectable virus four weeks after treatment with GS-7977 plus ribavirin ended.